For numerous applications it is desired to contain and/or temporarily prevent passage of aqueous waste or other aqueous materials and at some later time dispose of the barrier material in a clean and environmentally friendly manner. To be effective, the material used to temporarily prevent passage must provide a barrier to leakage and at the appropriate time desirably break up into components that facilitate suitable disposal while minimizing adverse effects on the environment. Uses for such latently separable barrier materials include bags or other containers for biological waste, agricultural mats of various kinds, and disposable items like single use beverage containers and the like. Prior attempts to provide such materials have included laminates of film barriers with water sensitive layers of, for example, polyvinyl alcohol. In use, the barrier contacts the liquid contents and prevents passage until the water sensitive layer is exposed to an aqueous environment. At that point the water sensitive layer dissolves, breaks up or otherwise separates to facilitate disposal. Disposal by flushing in conventional toilets is possible with some of these combinations. Difficulties have been identified with these prior materials because many water sensitive materials like polyvinyl alcohol become dimensionally unstable when exposed to conditions of moderate to high humidity and tend to weaken or stretch. In use as a container, for example, the material can stretch out of shape and/or weaken to the point of rupture. Attempts to add stability by increasing the barrier film thickness, for example, add unacceptable cost and/or increase the issues to be addressed upon disposal. The thicker films have a greater tendency to remain intact on flushing, for example, and clog toilets or downstream systems. The need continues, therefore, for a temporary barrier, latently dispersible material that is stable under use conditions but also easily disposable under aqueous conditions as by flushing, for example. The present invention addresses this and similar needs.
The present invention includes a latently dispersible barrier composite using a low strength barrier layer of water insoluble composition combined with a water sensitive, low strength carrier and on the opposing side of the carrier an inextensible, dispersible support layer. The layers are bonded and provide a barrier to aqueous liquid contact from one side but the combination disperses when contacted by aqueous liquid from the other side. In use as a container, cover, or the like, convenient and environmentally sensitive disposal may be achieved. Examples of barrier layers include films or fine fibers of very lightweight construction using polymers such as polylactic acid or polycaprolactone. Examples of water sensitive carrier webs include films of polyvinyl alcohol with or without other components. Examples of inextensible support materials include higher modulus or low stretch toilet tissue grades.
Where all component layers are biodegradable and/or dispersible, disposal is facilitated. For many applications it will be desirable to maintain component layers as light or low basis weight as is compatible with the intended use. In particular, the barrier layer may not be readily dispersible if it is of increased thickness. Cost will provide an incentive to reduce the weight of the component layers, particularly for single use applications. Many such applications will use a barrier layer of polylactic acid having a thickness in the range of from about 0.5 to about 2.0 microns, polyvinyl alcohol film carrier layer having a thickness in the range of from about 10 to about 50 microns, and a tissue support layer in the range of from about 10 to about 30 gsm, for example. As a result the composite will desirably have a hydrohead property of at least about 15 mbar, for some applications at least about 25 mbar, for more demanding applications at least about 50 mbar, and in some cases at least about 75 mbar. Bonding of the layers may be by a variety of means that preserve desired properties, including thermal (such as coextrusion or extrusion coating, for example) and adhesive, pattern and smooth bonding means.
As used herein unless the context requires a different meaning, the following terms have the meanings set forth below:
As used herein and in the claims, the term xe2x80x9ccomprisingxe2x80x9d is inclusive or open-ended and does not exclude additional unrecited elements, compositional components, or method steps.
As used herein the term xe2x80x9cnonwoven fabric or webxe2x80x9d means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).
As used herein the term xe2x80x9cmeltblown fibersxe2x80x9d means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers that may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting surface.
xe2x80x9cBonded carded webxe2x80x9d refers to webs made from staple fibers which are sent through a combing or carding unit, which breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. Such fibers are usually purchased in bales that are placed in a picker that separates the fibers prior to the carding unit. Once the web is formed, it then is bonded by one or more of several known bonding methods. One such bonding method is powder bonding, wherein a powdered adhesive is distributed through the web and then activated, usually by heating the web and adhesive with hot air. Another suitable bonding method is pattern bonding, wherein heated calender rolls or ultrasonic bonding equipment are used to bond the fibers together, usually in a localized bond pattern, though the web can be bonded across its entire surface if so desired. Another suitable and well-known bonding method, particularly when using bicomponent staple fibers, is through-air bonding.
xe2x80x9cAirlayingxe2x80x9d is a well-known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 6 to about 19 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air or a spray adhesive. Examples of airlaying technology can be found in U.S. Pat. Nos. 4,494,278, 5,527,171, 3,375,448 and 4,640,810.
As used herein, through-air bonding or xe2x80x9cTABxe2x80x9d means a process of bonding a nonwoven web containing adhesive polymeric component fibers, particles or the like in which air sufficiently hot to melt one of the polymers of which the fibers or particles of the web are made is forced through the web. The air velocity often is between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides the bonding. Through air bonding has relatively restricted variability and since through-air bonding (TAB) requires the melting of at least one component to accomplish bonding, it is restricted to webs with two components like conjugate fibers or those which include an adhesive. In the through-air bonder, air having a temperature above the melting temperature of one component and below the melting temperature of another component is directed from a surrounding hood, through the web, and into a perforated roller supporting the web. Alternatively, the through-air bonder may be a flat arrangement wherein the air is directed vertically onto the web. The operating conditions of the two configurations are similar, the primary difference being the geometry of the web during bonding. The hot air melts the lower melting polymer component and thereby forms bonds between the filaments to integrate the web.
As used herein, the term xe2x80x9cflushablexe2x80x9d means that an item may be successfully transported through a toilet and through the typical municipal sewerage system piping and pumps without incident (i.e. clogging).
As used herein, the term xe2x80x9cwater dispersiblexe2x80x9d refers to structures which when placed in an aqueous environment will, with sufficient time, break apart into smaller pieces. As a result, the structure once dispersed may be more advantageously processable in recycling processes or flushable in, for example, septic and municipal sewage treatment systems. If desired, such structures may be made more water dispersible or the dispersion may be hastened by the use of agitation and/or certain triggering means. The actual amount of time will depend at least in part upon the particular end-use design criteria.
As used herein, the term xe2x80x9cbiodegradablexe2x80x9d means that a material degrades from the action of naturally occurring microorganisms such as bacteria, fungi and algae.
As used herein, the term xe2x80x9ctissuexe2x80x9d includes not only inextensible, dispersible cellulose based tissue products, but other nonwoven webs having the described properties such as meltblown webs of meltblown PVOH fibers, for example. The manufacture of tissue grades of varying extensibility is well-known and may be obtained by conventional steps such as creping or wet microcontraction as more fully described, for example, in U.S. Pat. No. 6,270,875 incorporated herein in its entirety by reference. It includes layers that may become saturated and/or allow liquid to pass through, sometimes referred to as xe2x80x9csaturation layerxe2x80x9d.
As used herein, the term xe2x80x9cwater sensitivexe2x80x9d means a structure or layer that loses integrity in contact with water as by means of breaking up or dissolving, for example, but which maintains effective strength for the desired application.
As used herein, the term xe2x80x9cwater solublexe2x80x9d means dissolves into water as a homogeneous solution.
As used herein, the term xe2x80x9cinextensiblexe2x80x9d means having machine direction stretch of less than 15%. The following parameters may be used: crosshead speed: 10.0 in/min (254 mm/min), full scale load: 10 lb (4,540 g.), jaw span (the distance between the jaws, sometimes referred to as the gauge length): 2.0 inches (50.8 mm), specimen width: 3 inches (76.2 mm). The testing device may be a Sintech, Model CITS-2000 (Systems Integration Technology Inc. Stoughton, Mass.xe2x80x94a division of MTS Systems Corporation, Research Triangle Park, N.C.).
Tensile: As used herein, dry CD tensile strengths represent the peak load per sample width when a sample is pulled to rupture in the cross-machine direction. The sample must be dry and have been conditioned at 73.4xc2x13.6xc2x0 F., 50xc2x15% relative humidity for at least 4 hours prior to testing. Samples are prepared by cutting a 3-inch widexc3x976-inch long strip in the cross-machine direction (CD) orientation. The instrument used for measuring tensile strengths is an MTS Systems Synergie 100. The data acquisition software was MTS TestWorks(copyright) 3.10 (MTS Systems Corp., Research Triangle Park, N.C.). The load cell is selected from either a 50 Newton or 100 Newton maximum, depending on the strength of the sample being tested, such that the majority of peak load values fall between 10-90% of the load cell""s full scale value. The gauge length between jaws is 4+/xe2x88x920.04 inches. The jaws are operated using pneumatic-action and are rubber coated. The minimum grip face width is 3 inches and the approximate height of the grip face of the jaw is 1.0 inch. The crosshead speed is 10+/xe2x88x920.4 inches/min. The sample is placed in the jaws of the instrument, centered both vertically and horizontally. The test is then started and ends when the specimen breaks. The peak load is recorded as the xe2x80x9cCD dry tensile strengthxe2x80x9d of the specimen. Five (5) representative specimens are tested for each product and the arithmetic average of all five individual specimen tests is the CD tensile strength for the product.
Wet tensile strength measurements are measured in the same manner, but after the center portion of the previously conditioned sample strip has been saturated with distilled water immediately prior to loading the specimen into the tensile test equipment. Sample wetting is performed by first laying a single test strip onto a piece of blotter paper (Fiber Mark, Reliance Basis 120). A pad is then used to wet the sample strip prior to testing. The pad is a green, Scotch-Brite brand (3M) general-purpose commercial scrubbing pad. To prepare the pad for testing, a full-size pad is cut approximately 2.5 inches long by 4 inches wide. A piece of masking tape is wrapped around one of the 4-inch long edges. The taped side then becomes the xe2x80x9ctopxe2x80x9d edge of the wetting pad. To wet a tensile strip, the tester holds the top edge of the pad and dips the bottom edge in approximately 0.25 inches of distilled water located in a wetting pan. After the end of the pad has been saturated with water, the pad is then taken from the wetting pan and the excess water is removed from the pad by lightly tapping the wet edge three times across a wire mesh screen. The wet edge of the pad is then gently placed across the sample, parallel to the width of the sample, in the approximate center of the sample strip. The pad is held in place for approximately one second and then removed and placed back into the wetting pan. The wet sample is then immediately inserted into the tensile grips so the wetted area is approximately centered between the upper and lower grips. The test strip should be centered both horizontally and vertically between the grips. (It should be noted that if any of the wetted portion comes into contact with the grip faces, the specimen must be discarded and the jaws dried off before resuming testing.) The tensile test is then performed and the peak load recorded as the CD wet tensile strength of this specimen. As with the dry CD tensile test, the characterization of a product is determined by the average of five representative sample measurements. MD results may be obtained by cutting and loading the samples in the MD direction.
MD Extensibility: is the stretch at peak load defined as the elongation of a specimen at the point at which it generates its peak load divided by the gauge length expressed as a percent.
Modulus: A measure of stiffness of a web as determined by Max Slope which is the maximum slope of the machine direction load/elongation curve for the web. The tensile tester program should be set up such that five hundred points such as P1 and P2 are taken over a two and one-half inch (63.5 mm) span of elongation. This provides a sufficient number of points to exceed essentially any practical elongation of the specimen. With a ten inch per minute (254 mm/min) crosshead speed, this translates into a point every 0.030 seconds. The program calculates slopes among these points by setting the 10th point as the initial point (for example P1), counting thirty points to the 40th point (for example, P2) and performing a linear regression on those thirty points. It stores the slope from this regression in an array. The program then counts up ten points to the 20th point (which becomes P1) and repeats the procedure again (counting thirty points to what would be the 50th point (which becomes P2), calculating that slope and also storing it in the array). This process continues for the entire elongation of the sheet. The Max Slope is then chosen as the highest value from this array. The units of Max Slope are kg per three-inch specimen width. (Strain is , of course, dimensionless since the length of elongation is divided by the length of the jaw span. This calculation is taken into account by the testing machine program.)
Hydrohead: A measure of the liquid barrier properties of a fabric is the hydrohead test. The hydrohead test determines the millibars of water pressure that the fabric will support before a predetermined amount of liquid passes through. A fabric with a higher hydrohead reading indicates it has a greater barrier to liquid penetration than a fabric with a lower hydrohead. The hydrohead test is performed according to Federal Test Standard 191A, Method 5514 except that no support was used, and the measure was taken at the first drop of penetration.
Flushability Testing
Materials
A 312 in2flushable commode liner fabricated by sealing two halves in trapezoid shape with a long side of 24 inches and a short side of 3.5 inches to form a bag open at the long side.
Saline (300 ml per test)
Toilet Paper (10 standard commercial grade sheets per test)
1.6 gallon standard flush toilet having a water surface about 12 inchesxc3x9710 inches with a minimum ball pass diameter of 2 inches (ANSI AI12.19.2, 1973). The siphoning trapway is located at the rear of the bowl and flushing water is provided by a gravity discharge tank. Dimensions are about 4 inch diameter for discharge outlet at the bottom of the bowl, which is also the entrance to the trapway, and the diameter of the trapway itself, at around 2.5 inches.
A simulated lateral system was constructed using clear plastic pipe in a zigzag run connected to the toilet. The diameter of the pipe is four inches, with an overall run length of about 45 feet and a downward slope of about xc2xcxe2x80x3 per foot. The pipes wind around in a rectangular pattern, like the winding of multiple flights in rectangular stair well or like the coils in a square spring. A four-foot run from under the toilet turns 90 degrees at an elbow, then a 3-foot run of pipe, another 90-degree elbow, a 10 foot run, a 90-degree elbow, a 3-foot run, a 90-degree elbow, a 10-foot run, a 90-degree elbow, a 3-foot run, a 90-degree elbow, and a final 10-foot run before a final turn and outlet onto a screen (4-e-3-e-10-e-3-e-10-e-3-e-10-turn to outlet).
Procedure
1. Pour 300 ml of saline into commode liner
2. Place 10 sheets of toilet paper into liner
3. Drop filled commode liner into 1.6-gallon toilet
4. Allow approximately 10 seconds for commode liner to sink to bottom of bowl
5. Flush Toilet
6. Observe that commode liner passes through lateral piping system and does not become clogged.
Pass Criteria
The commode liner is considered flushable if the commode liner flushes in 2 flushes or less, nine out of ten times. The commode liner must also pass through the lateral piping system without clogging. The commode liner need not pass through the lateral piping system in only 2 flushes but must show continued movement down the lateral system with each flush, and eventually reach the outlet.
Dispersibility
Commode liners were flushed and then observed as they were put through a municipal sewage-treatment transport simulator. The simulator is a tank of about 30 gallons of water with recirculating pumps to mimic hydraulic flow rates of about two feet per second, which are comparable to general conditions seen in travel through the sewer line to a sewage treatment plant. After ninety minutes the simulator was drained of water through a screened outlet, and any sections caught on the screen were recovered. These sections were then measured to determine their total mass. The total area of a commode liner is 312 in2, and it is considered dispersed if no more than about 30%, desirably no more than about 25%, and more desirably no more than about 15% of the original barrier layer mass is left. Ninety minutes is considered the minimum travel time from the home to the treatment facility.
Materials
Standard 312 in2 commode liner
1.6 gallon toilet as described above.
Lateral piping system as described above
Transport Simulator: as described.
Ruler
Procedure
1. Fill transport simulator with water up to fill line
2. Turn transport simulator on
3. Set lateral piping valve to pass on to transport simulator
4. Drop commode liner into 1.6-gallon toilet (saline and toilet tissue are included)
5. Flush toilet and observe as commode liner passes through lateral piping
6. The commode will then drop into the transport simulator
7. Allow commode liner to circulate for 90 minutes
8. Turn off simulator
9. Remove undissolved sections of PLA that are visible or floating. Be careful not to damage the sections and keep them separate from one another to avoid sticking.
10. Drain out water
11. Remove remaining pieces of PLA.
12. Unravel PLA pieces (drying is optional)
13. Record areas of PLA pieces and mass based on area determination and multiplying by prewet basis weight.
14. Clean up circular transport tester